Preheat oven to 375°F (190°C).
In a large oven-safe skillet, brown the ground meat over medium-high heat, breaking it up as it cooks.
Add diced onion, bell pepper, jalapeño, and garlic to the skillet. Cook for 5-7 minutes until vegetables are softened.
Stir in chili beans, black beans, tomato sauce, chili powder, black pepper, cumin, and red pepper flakes. Simmer for 10-15 minutes until flavors are well combined.
While chili simmers, whisk together cornmeal, flour, baking powder, sugar, and salt in a large bowl.
In a separate bowl, beat eggs, then whisk in milk and vegetable oil.
Pour wet ingredients into dry ingredients and stir until just combined (don't overmix).
Spoon cornbread batter evenly over the chili in the skillet.
If using, brush cornbread topping with melted butter and sprinkle with cheese.
Bake for 30-35 minutes until cornbread is golden brown and a toothpick inserted in cornbread comes out clean.
Let casserole sit for 5 minutes before serving.